How to type command to running process in Python?

I want to control running process/program by script in Python.
I have a program linphonec (You can install: apt-get install linphonec).
My task is:
1. Run linphonec (I'm using subprocess at the moment)
2. When linphonec is running it has a many command to control this and I want to e.g use "proxy list" <- this is command in linphonec.